A position sensor can detect the presence and location of a touch by a finger or by an object, such as a stylus, within an area of an external interface of the position sensor. In a touch sensitive display application, the position sensor enables, in some circumstances, direct interaction with information displayed on the screen, rather than indirectly via a mouse or touchpad. Position sensors can be attached to or provided as part of devices with displays. Examples of devices with displays include, but are not limited to, computers, personal digital assistants, satellite navigation devices, mobile telephones, portable media players, portable game consoles, public information kiosks, and point of sale systems. Position sensors have also been used as control panels on various appliances.
There are a number of different types of position sensors and touch screens. Examples include, but are not limited to resistive touch screens, surface acoustic wave touch screens, capacitive touch screens, and the like. A capacitive touch screen, for example, may include an insulator coated with a transparent conductor in a particular pattern. When an object, such as a finger or a stylus, touches the surface of the screen there may be a change in capacitance. This change in capacitance may be measured by a controller to determine where the touch occurred on the touch screen.
In a mutual capacitance configuration, for example, an array of conductive drive electrodes or lines formed on one surface of an insulator and conductive sense electrodes or lines formed on an opposite surface of an insulator can be used to form a touch screen having capacitive nodes. A node may be formed where a drive electrode and a sense electrode overlap. The electrodes may be separated by an insulator to avoid electrical contact. The sense electrodes may be capacitively coupled with the drive electrodes at the nodes. A pulsed or alternating voltage applied on a drive electrode may therefore induce a charge on the sense electrodes that overlap with the drive electrode. The amount of induced charge may be susceptible to external influence, such as from the proximity of a nearby finger. When an object touches the surface of the screen, the capacitance change at each node on the grid can be measured to determine the position of the touch.
In a conventional touch screen as shown in FIG. 1, drive electrodes 104(X) and sense electrodes 105(Y) may be formed of solid portions of ITO. Sensing area 110 of the position sensing panel 101, denoted by the dotted line, encompasses a number of the nodes 111 formed where the drive electrodes 104(X) and sense electrodes 105(Y) overlap. In the example, the gaps between adjacent X electrode bars may be made narrow. This may enhance the ability of the electrodes 104(X) to shield against noise arising from an underlying display 2 such as that shown in FIG. 3. In some examples, 90% or more of the sensing area 110 may be covered by ITO. In an example such as that shown in FIG. 1, the gap between adjacent drive electrodes 104(X) may be 200 microns or less.
In the example of FIG. 1, the sensing area 110 of the position sensing panel 101 and the region of the display 2 as shown in FIG. 3 visible through the position sensing panel 101 may cover a similar area. As such, the visible region of the display 2 may be denoted by the dotted line of area 110 in FIG. 1.
In one example, each drive electrode 104(X) forms nodes with a number of the sense electrodes 105(Y) on an adjacent plane. As mentioned previously, there may be nodes 111 formed where the drive electrodes 104(X) overlap the sense electrodes 105(Y).
A number of drive electrode connecting lines 112 may be in communication with a number of drive electrodes 104(X). A number of sense electrode connecting lines 113 may be in communication with a number of sense electrodes 105(Y). The patterns of the connecting lines 112 and 113 are shown by way of an example only. In the example shown in FIG. 1, the drive electrode connecting lines 112 and the sense electrode connecting lines 113 may be connected to a control unit 120.
A change in capacitance may occur when an object touches the surface of the panel 101. In some examples, the change in capacitance at the node 111 may be sensed by the control unit 120. The control unit 120 applies pulsed or alternating voltages to the drive electrodes 104(X) through the drive electrode connecting lines 112. The control unit 120 measures the amount of charge induced on the sense electrodes 105(Y) through the sense electrode connecting lines 113. The control unit 120 determines that a touch may have occurred and calculates the location of the touch based upon the changes in capacitance sensed at one or more of the nodes 111.
In the example of FIG. 1, the drive electrode connecting lines 112 and the sense electrode connecting lines 113 may be arranged in separate non-overlapping regions of the position sensing panel 101.
FIG. 2 illustrates the arrangement of drive electrode connecting lines 112 and the sense electrode connecting lines 113 in the example of FIG. 1 in more detail. In this example, the sense electrode connecting lines 113 and the drive electrode connecting lines 112 may be provided on opposed faces 103a and 103b of the substrate 103. The sense electrode connecting lines 113 and the drive electrode connecting lines 112 may be arranged in different regions of the substrate so that the drive electrode connecting lines 112 and the sense electrode connecting lines 113 may not overlap one another and may not be in close proximity to one another.
As is explained above, in some examples, the control unit 120 applies pulsed or alternating voltages to the drive electrodes 104(X) through the drive electrode connecting lines 112, measures the amount of charge induced on the sense electrodes 105(Y) through the sense electrode connecting lines 113, and determines that a touch may have occurred and the location of the touch based upon the sensed changes in capacitance. If capacitive coupling was to occur between a drive electrode connecting line 112 and a sense electrode connecting line 113, this could result in the pulsed or alternating voltages applied to the drive electrode connecting line 112 inducing charges in the sense electrode connecting line 113, which may cause a false determination that a touch may have occurred, or a miscalculation of the location of a touch. In some examples, the sense electrode connecting lines 113 and the drive electrode connecting lines 112 may be spaced apart to prevent capacitive coupling between the sense electrode connecting lines 113 and the drive electrode connecting lines 112.